Method of manufacturing a semiconductor device

ABSTRACT

A low thermal conductivity layer is formed on a back surface of a semiconductor wafer or chip, and a laser impression is formed on the low thermal conductivity layer. The laser impression can be formed without damaging the device surface of the semiconductor wafer or chip due to exothermic heat of the laser impression.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of manufacturing asemiconductor device, and more particularly to a method of manufacturinga wafer-level chip size package (WCSP).

The present application claims priority under 35 U.S.C. §119 to JapanesePatent Application No. 2001-155148, filed May 24, 2001, which is hereinincorporated by reference in its entirety for all purposes.

2. Description of the Related Art

The WCSP is one of semiconductor mold packages, a that has simplepackaging. A plurality of pads are constructed for a plurality ofsemiconductor chips, are formed on a silicon substrate at thewafer-level. Then, bump electrodes for an assembly are formed, afterwiring patterns connecting the pads are formed. Next, solder balls forpackaging are formed on the bump electrodes. Finally, the wafer-levelsilicon substrate is divided into chip size pieces. At this time,between the pads, the wiring patterns and the bump electrodes areelectrically connected by using solder balls, for instance. Similarly toother types of mold packages, such as a ball grid array (BGA) and a chipsize package (CSP), manufacturing of the WCSP, is performed as anassembly process.

Since such a WCSP is a commodity transacted at the wafer-level as wellas the chip size level, both of the chip size and wafer levels areimpressed with a commodity description or identification. Commonly,since the pads, the wiring patterns and the bump electrodes are formedon a device surface of the silicon substrate, an impression for the WCSPis performed on a back surface which is opposite from the devicesurface. A conventional impression method for the WCSP, method is stampprinting using a rubber-stamp. However, the stamp printing has a fewdisadvantages, for example wear of the stamp and changing of ink. Also,a laser impression that is to be applied to another mold package must beset up, a slowing the process and increasing cost.

At the back surface of a conventional WCSP, since no resist is appliedafter back-grinding of the WCSP, the silicon substrate is barely formed.When the laser impression is formed in such a WCSP, thermal energy oflaser light is conducted at the device surface (a surface of integratedcircuit), whereby aluminum wiring is damaged and bonding betweenaluminum pads and wiring patterns may be destroyed.

SUMMARY OF THE INVENTION

The present invention is therefore directed to providing a method ofmanufacturing a semiconductor device, which substantially overcome oneor more of the problems due to the limitations and disadvantages of therelated art.

It is an objective of the invention to provide a semiconductor deviceand a method of manufacturing the same, whereby a laser impression isformed on, the semiconductor device without any negative effects on thedevice surface of the semiconductor wafer (chip) due to exothermic heatgenerated during formation of the laser impression.

To achieve the above noted and other objects, a semiconductor device anda method of manufacturing the same of the present invention includesforming a low thermal conductivity layer on the back surface of thesemiconductor wafer (chip), and the laser impression is formed on thelow thermal conductivity layer.

According to the present invention, the laser impression can be formedwithout damaging the device surface of the semiconductor wafer (chip).

The above and further objects and novel features of the invention willmore fully appear from the following detailed description, appendedclaims and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing outand distinctly claiming the subject matter which is regarded as theinvention, it is believed that the invention, the objects and featuresof the invention and further objects, features and advantages thereofwill be better understood from the following description taken inconnection with the accompanying drawings in which:

FIG. 1 is an oblique perspective illustration showing a semiconductordevice according to a first preferred embodiment of the presentinvention;

FIG. 2 is a cross-sectional view showing the semiconductor deviceaccording to the first preferred embodiment of the present invention;

FIGS. 3(a) through 3(h) are cross-sectional views showing a method ofmanufacturing the semiconductor device according to the first preferredembodiment of the present invention;

FIG. 4 is an explanation diagram showing formation of a laser impressionaccording to the first preferred embodiment of the present invention;and

FIGS. 5(a) through 5(c) are cross-sectional views showing an example ofmanufacturing method of a low thermal conductivity layer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will hereinafter bedescribed in detail with reference to the accompanying drawings. Thedrawings used for this description typically illustrate majorcharacteristic parts in order that the present invention will be easilyunderstood.

FIG. 1 is an oblique perspective illustration showing a semiconductordevice 100 according to a first preferred embodiment of the presentinvention. FIG. 2 is a cross-sectional view showing the semiconductordevice 100 according to the first preferred embodiment of the presentinvention. The semiconductor device 100 includes a semiconductor chip10, a pad electrode 12, a wiring pattern 14, a protection layer 16, aninsulating layer 18, a bump electrode 20, resin 22, a solder ball 24, alow thermal conductivity layer 26 and an impression 28. Thesemiconductor chip 10 indicates a semiconductor substrate having anintegrated circuit 11. The pad electrode 12 is formed on thesemiconductor chip, and electrically connected to the integratedcircuit. Such a pad electrode 12 may be an aluminum or an aluminum alloyfor example. The pad electrode 12 may be a copper or a copper alloy forexample and is electrically connected to the bump electrode 20, throughthe wiring pattern 14 may be a copper or a copper alloy. The protectionlayer 16 protecting a device region may be a nitride layer for example,and is formed on the semiconductor chip 10 as having openings exposingthe pad electrode 12. The insulating layer 18 may be a polyimide forexample, and is formed on the protection layer 16 as having openingsexposing the pad electrode 12 as well as the protection layer 16. As aresult, the pad electrode 12 is exposed through the openings of theprotection layer 16 and the insulating layer 18.

The wiring pattern 14 and the bump electrode 20 are formed over theinsulating layer 18, and are electrically connected to the pad electrode12. Areas surrounding the wiring pattern 14 and the bump electrode 20are sealed by the resin 22, however a part of the bump electrode 20 maybe exposed. The solder ball 24 as a metal electrode is formed on theexposed region of the bump electrode 20.

The semiconductor chip 10 has a device surface including the integratedcircuit 11, the pad electrode 12 and the wiring pattern 14, and a backsurface which is opposite from the device surface. The low thermalconductivity layer 26 is formed on the back surface of thesemiconductors chip 10. As shown in FIG. 1, the impression 28 whichindicates, for example a company name, a product name or a serialnumber, is impressed on the exposed surface of the low thermalconductivity layer 26 by using a laser. Since the resin 22 and the lowthermal conductivity layer 26 are not formed on a side surface of thesemiconductor chip 10, the side surface of the semiconductor chip 10 isexposed.

Next, a method of manufacturing such a semiconductor device will bedescribed with reference to FIGS. 3(a) through 3(h).

FIGS. 3(a) through 3(h) are cross-sectional views showing a method ofmanufacturing the semiconductor device 100 according to a firstpreferred embodiment of the present invention. A semiconductor wafer 30is a disciform substrate obtaining by slicing a disciform silicon ingotwhich is formed by a czochralski method (e.g. a C-Z method). Integratedcircuits 11 are formed on the device surface of the semiconductor wafer30.

As shown in FIG. 3(a), the pad electrodes 12 which are electricallyconnected to the integrated circuit 11, is formed on the semiconductorwafer 30. The, protection layer 16 protecting the integrated circuit 11and having openings 17 corresponding to locations of the pad electrodes12, is formed on the semiconductor wafer 30. And, the insulating layer18 having openings 19 corresponding to locations of the pad electrodes12, is formed on the protection layer 16. The insulating layer 18 may bea polyimide for example.

Next, as shown in FIG. 3(b), a resist, pattern 32 exposing the padelectrodes 12 and portions of insulating layer 18 is formed over thesemiconductor wafer 30. The resist patterns 32 are used asia maskpattern when the wiring pattern 14 is formed at a following processstep.

Next, as shown in FIG. 3(c), the wiring patterns 14 may be a copper forexample, are formed on the basis of the resist pattern 32 by using anelectrolytic plating. Thickness and width of the wiring patterns 14 are5 μm, respectively. The wiring patterns 14 are electrically connected tothe pad electrode 12 in the openings.

Next, as shown in FIG. 3(d), a resist pattern 34 exposing parts of thewiring patterns 14, is formed over the semiconductor wafer 30 after theresist pattern 32 is removed. A thickness of the resist pattern 34 isabout 100 μm. Bump electrodes 20 are formed at locations correspondingto exposed parts of the wiring patterns 14 by using the resist pattern34. The bump electrodes 20 may be a copper for example, and may beformed by electrolytic plating so as to electrically connected to thewiring patterns 14 at the exposed parts of the wiring patterns 14. Theresist pattern 34 is removed after the bump electrodes 20 are formed.

Next, as shown in FIG. 3(e), the device surface of the semiconductorwafer 30 including the wiring patterns 14 and the bump electrodes 20 issealed by a resin 22. At this time, the resin 22 covers the wiringpatterns 14 and the bump electrodes 20.

A thickness of the resin 22 is about 150 μm, and a thickness of theresin 22 on the bump electrode 20 is about 50 μm.

Next, as shown in FIG. 3(f), a surface of the resin 22 is ground byusing, for example a grinding blade until the bump electrodes 20 areexposed. Solder balls 24 are formed on the exposed surfaces of the bumpelectrodes 20. The solder balls 24 are used as metal electrodes forpackaging.

Next, as shown in FIG. 3(g), the back surface of the semiconductor wafer30 which is opposite from the device surface is ground. Then, the lowthermal conductivity layer 26 is formed on the ground back surface. Suchgrinding of the back surface is called a back-grind process.

Next, as shown in FIG. 3(h), the semiconductor wafer is divided intoplural chip size devices by using a diamond blade for example. Finally,the impression 28 including various characters (company and productname, a serial number, and so on), is impressed on the low thermalconductivity layer 26 which is formed on the ground back surface of theplurality of chip size devices by using a laser impression method.

In the first preferred embodiment of the present invention, since thelow thermal conductivity layer 26 is formed after the device surface ofthe semiconductor wafer 30 is sealed by the resin 22, the low thermalconductivity layer 26 can be formed as having an impression thereonwithout damaging the device surface.

FIG. 4 is an explanation diagram showing a method of a laser impressionaccording to the first preferred embodiment of the present invention. Asshown in FIG. 4, the laser impression is performed by using a laseroscillator 36, for example a yttrium aluminum garnet (YAG) laser. Alaser light 38 which is output from the laser oscillator 36 is reflectedby a mirror 40, and then exposed on the back surface of thesemiconductor chip 10 (the semiconductor device) having the low thermalconductivity layer 26 thereon. Specifically, the impression 28 includingvarious characters is impressed on the low thermal conductivity layer 26by a scan in response to a movement of the mirror 40 (e.g. a porigonmirror). On the other hand, the impression process may also be performedby a transcription of the various characters which are carved on a glassmask. Specifically, the various characters are transcribed on the lowthermal conductivity layer 26 by using such a glass mask as a mask, whenthe laser light 38 is exposed on the low thermal conductivity layer 26.

In the first preferred embodiment of the present invention, anirradiation condition of such a laser is described below. It should beunderstood that the following conditions are provided as an example andshould not be constructed as limiting, since different conditions may beused to create the laser impression without damaging the chip on whichlow thermal conductivity layer 26 is formed.

-   -   (1) A laser type is a yttrium aluminum garnet laser (YAG laser).    -   (2) A wavelength of the YAG laser is 106/m.    -   (3) A strength of the YAG laser is between 740 mJ through 800        mJ.    -   (4) A scan type of the YAG laser is a 10 kHz flasher.    -   (5) A scan speed of the YAG laser is between 100 ms/m through        300 ms/m.

Next, a detailed description of the low thermal conductivity layer 26will be given below. The low thermal conductivity layer 26 has a lowthermal conductivity, and is possible to impress characters thereonusing a thermal print having a low energy. Specifically, the low thermalconductivity layer 26 has a thermal conductivity lower than that of thesemiconductor substrate which may be a silicon for example. Since thethermal conductivity of the low thermal conductivity layer 26 isrelatively lower than that of the substrate, an impression may be formedon the low thermal conductivity layer 26 using a lower energy. The lowthermal conductivity layer 26 as covered on the device surface havingthe integrated circuit prevents thermal conductance of heat generatedduring formation of the laser impression.

The favorable thermal conductivity as such a low thermal conductivitylayer 26 is, for example between 10×10⁻⁴ (W/m·K) through 10×10⁻²(W/m·K), since the thermal conductivity of the silicon is 138.13956W/m·K (0.33 cal/cm sec·° c.). In the first preferred embodiment, themost favorable thermal conductivity of the low thermal conductivitylayer 26 is between 0.10×10⁻⁴ (W/m·K) through 25×10⁻⁴ (W/m·K). By theway, a printing energy needed to form the impression must increase whensuch a thermal conductivity is less than 10×10⁻⁵ (W/m·K). Also, thethermal conductance on the device surface occurs more easily when such athermal conductivity is more than 10×10 ⁻² (W/m·K). As a result, adissolution and a peeling of various connections at the pad electrodes12 for example, the wiring patterns 14, the bump electrodes 20 and thesolder balls 24 for example, occur more easily. Furthermore, the wiringpattern 14 is easier to dissolve and peel. The thermal conductivity inthe first preferred embodiment indicates various layer's thermalconductivity.

The low thermal conductivity layer 26 may be for example an epoxy resin,a polyethylene resin, a polyester resin, a polyimide resin or apolyurethane resin, as used in a normal packaging process. Also, athickness of the low thermal conductivity layer 26 is selected inaccordance with the packaging type, for example equal to or more than 50μm. In the first preferred embodiment, the most favorable thickness ofthe low thermal conductivity layer 26 is between 100 μm through 200 μm.

The low thermal conductivity layer 26 may be formed by coating using aliquid (paste) material, and also by bonding using a film material. Thelow thermal conductivity layer 26 can be formed fast, by using suchforming processes. The coating using a liquid (paste) material issuitable for forming a uniform layer quickly for a comparatively largewafer. On the other hand, the bonding using a film material is suitablefor forming a low thermal conductivity layer quickly and cheaply, sincemanagement of such a material is easy and requires simple installation.

As such a coating method, there are, for example a spin coating methodusing a spinner and a paint coating method by using movement of adispenser. The spin coating method using such a spinner is suitable forforming a uniform layer. On the other hand, the paint coating methodusing a dispenser is suitable for forming a uniform layer selectively onthe semiconductor substrate. Furthermore, other coating methods includea blade coating method, a wire bar coating method, a spray coatingmethod, a bead coating method, an air knife coating method, a curtaincoating method, and a coating method which provides a liquid (paste)material down a metal mold setting on the semiconductor substrate. Thelow thermal conductivity layer 26 is indurate or hardened by pressing, aheating or a light irradiation (e.g. ultraviolet rays).

On the other hand, bonding methods using such a film material may usefor example a thermal indurative adhesive (e.g. an epoxy adhesive), alight indurative adhesive or an adhesive tape. These bonding methods aresuitable for forming the layer quickly and cheaply.

The thermal conductivity of the low thermal conductivity layer 26 isadjustable by way of section of the above noted various materials. Next,a first example using an epoxy resin as a material is described. Thepaste epoxy resin is seeped on the back surface of the semiconductorwafer 30 illustrated in FIG. 3(f) for example. Then, the seeped epoxyresin is uniformly spread until a thickness of the epoxy resin is about200 μm. Next, the semiconductor wafer 30 is put into an electricfurnace, and heated within a range of 160° c.˜180° c. As a result, theepoxy resin as the low thermal conductivity layer 26 as illustrated inFIG. 3(g) for example, is indurate and formed. The thermal conductivityof such a low thermal conductivity layer 26 is about between418.605×10⁻⁴ W/m·K through 9209.31×10⁻⁴ W/m·K (between 10×10⁻⁴cal/cm·sec·° c. through 22×10⁻⁴ cal/cm·sec·° c.).

Next, a second example using a metal mold is described below. The pasteepoxy resin is provided down the metal mold setting on the back surfaceof the semiconductor substrate 30. Then, the metal mold is compressedtogether until a thickness of the epoxy resin is about 200 μm. Next, thesemiconductor wafer 30 is put into an electric furnace, and heatedwithin a range of 160° c.˜180° c. As a result, the epoxy resin as thelow thermal conductivity layer 26 is indurate and formed. The thermalconductivity of such a low thermal conductivity layer 26 is also aboutbetween 418.605×10⁻⁴ W/m·K through 9209.31×10⁻⁴ W/m·K (between 10×10⁻⁴cal/cm·sec·° c. through 22×10⁻⁴ cal/cm·sec·° c.).

Next, a third example using an indurative ink which is indurate byultraviolet irradiation (an UV ink) is described below. The UV ink isseeped on the back surface of the semiconductor wafer 30. Then, theseeped epoxy resin is uniformly spread until a thickness of the epoxyresin is about 200 μm. Next, the semiconductor wafer 30 is put into anelectric furnace, and heated within a range of 160° C. ˜180 ° c. As aresult, the UV ink as the low thermal conductivity layer 26 is indurateand formed. The thermal conductivity of such a low thermal conductivitylayer 26 is about between 418.605×10⁻⁴ W/m·K through 8372.1×10 W/m·K(between 1×10⁻⁴ cal/cm·sec·° c. through 20×10⁻⁴ cal/cm·sec·° c.).

Next, a fourth example using an epoxy adhesive 52 and a low lightpermeable film 54, for example a polyester film and polyethylene film,is described below. FIGS. 5(a) through 5(c) are cross-sectional viewsshowing an example of a manufacturing method of the low thermalconductivity layer 26. The low light permeable film 54 does not includea carbon and an aluminum.

As shown in FIG. 5(a), the epoxy adhesive 52 is coated on the backsurface of the semiconductor wafer 30. Then, as shown in FIG. 5(b), thelow light permeable film 54 is superimposed on the epoxy adhesive 52.Next, the semiconductor wafer 30 is put into an electric furnace, andheated to about 150° C. As a result, as shown in FIG. 5(c), the epoxyadhesive 52 and the low light permeable film 54 are bonded, and the lowthermal conductivity layer 26 is formed. The thermal conductivity ofsuch a low thermal conductivity layer 26 is about between 2093.025×10⁻⁴W/m·K through 9209.31×10⁻⁴ W/m·K (between 5×10⁻⁴ cal/cm·sec·° c. through22×10 ⁻⁴ cal/cm·sec·° c.).

According to the first preferred embodiment of the present invention,since the low thermal conductivity layer 26 does not readily conductheat is formed on the back surface of the semiconductor chip 10, theheat of the laser light 38 as illustrated in FIG. 4, is concentrated atthe laser irradiation area of the low thermal conductivity layer 26.Since the laser irradiation area of the layer 26 is dissolved, animpression can be formed using a low energy. Furthermore, since the lowthermal conductivity layer 26 is formed after a back-grinding process ofthe semiconductor wafer 30 (the semiconductor chip 10), a better lowthermal conductivity layer 26 can be formed without surface concavityand convexity and an interfusion of foreign particle into the layer 26.

As a result, dissolution and peeling between the pad electrodes 12 andthe wiring patterns 14, the wiring patterns 14 and the bump electrodes20, and the bump electrodes 20 and the solder balls 24, can beprevented. Also, the dissolution and peeling of the wiring patterns 14can be avoided. Furthermore, the integrated circuit which is formed inthe device surface of the semiconductor chip 10 can be prevented frombeing destroyed. Therefore, the laser impression can be formed without anegative effect on the device surface of the semiconductor chip 10 dueto exothermic heat of the laser impression.

While the first preferred embodiment of the present invention presentsan example in which the laser impression is formed after thesemiconductor wafer 30 is divided into plural semiconductor chips 10,the present invention is not limited to this example and the laserimpression may be formed prior to dividing the semiconductor wafer 30.Therefore, the commodity transaction with the wafer-level as well as thechip size level can be fulfilled.

Further, while the first preferred embodiment of the present inventionpresents an example in which the low thermal conductivity layer 26 isformed on the entire back surface of the semiconductor wafer 30 (thesemiconductor chip 10), the present invention is not limited to thisexample and the low thermal conductivity layer 26 may be only formed onthe impression area of the back surface.

As described above, the semiconductor device and the method ofmanufacturing the same according to the present invention can form alaser impression without damaging the device surface of thesemiconductor chip.

The present invention has been described with reference to illustrativeembodiments, however, this invention must not be considered to beconfined only to the embodiments illustrated. Various modifications andchanges of these illustrative embodiments and the other embodiments ofthe present invention will become apparent to those skilled in the artwith reference to the description of the present invention. It istherefore contemplated that the appended claims will cover any suchmodifications or embodiments as fall within the true scope of theinvention.

1-24. (canceled)
 25. A method of manufacturing a semiconductor devicecomprising: providing a semiconductor substrate having a first surfaceand a second surface which is opposite the first surface, wherein thefirst surface of the semiconductor substrate includes a pad electrode;forming a first insulating layer which covers the first surface of thesemiconductor substrate and exposes the pad electrode; forming a secondinsulating layer which covers the first insulating layer and exposes thepad electrode; grinding the second surface of the semiconductorsubstrate; forming a low thermal conductivity layer including a lowlight permeable film, on the ground second surface of the semiconductorsubstrate; dividing the semiconductor substrate into pluralsemiconductor chip pieces; and forming a laser impression on the lowthermal conductivity layer of the plural semiconductor chip pieces. 26.The method of manufacturing according to claim 25, further comprisingforming a ball electrode on an exposed top of the pad electrode.
 27. Themethod of manufacturing according to claim 25, wherein said forming alow thermal conductivity layer comprises coating a liquid material onthe ground second surface of the semiconductor substrate.
 28. The methodof manufacturing according to claim 25, wherein said forming a lowthermal conductivity layer comprises bonding a film material on theground second surface of the semiconductor substrate using an adhesive.29. The method of manufacturing according to claim 25, wherein the lowthermal conductivity layer has a thermal conductivity within a range of5×10⁻⁴ W/m·K˜22×10⁻⁴ cal/cm·sec·° C.
 30. The method of manufacturingaccording to claim 25, wherein the laser impression is a product name.31. The method of manufacturing according to claim 25, wherein the laserimpression is a product number.
 32. The method of manufacturingaccording to claim 25, wherein the laser impression is a company name.33. The method of manufacturing according to claim 25, wherein the laserimpression is a serial number.
 34. A method of manufacturing asemiconductor device comprising: providing a semiconductor substratehaving a first surface and a second surface which is opposite the firstsurface, wherein the first surface of the semiconductor substrateincludes a pad electrode; forming a first insulating layer which coversthe first surface of the semiconductor substrate and exposes the padelectrode; forming a second insulating layer which covers the firstinsulating layer and exposes the pad electrode; grinding the secondsurface of the semiconductor substrate; forming a low thermalconductivity layer including a low light permeable film, on the groundsecond surface of the semiconductor substrate; forming a laserimpression on the low thermal conductivity layer; and dividing thesemiconductor substrate having the laser impression into pluralsemiconductor chip pieces.
 35. The method of manufacturing according toclaim 34, further comprising forming a ball electrode on an exposed topof the pad electrode.
 36. The method of manufacturing according to claim34, wherein said forming a low thermal conductivity layer comprisescoating a liquid material on the ground second surface of thesemiconductor substrate.
 37. The method of manufacturing according toclaim 34, wherein said forming a low thermal conductivity layercomprises bonding a film material on the ground second surface of thesemiconductor substrate using an adhesive.
 38. The method ofmanufacturing according to claim 34, wherein the low thermalconductivity layer has a thermal conductivity within a range of 5×10⁻⁴W/m·K˜22×10⁻⁴ cal/cm·sec·° C.
 39. The method of manufacturing accordingto claim 34, wherein the laser impression is a product name.
 40. Themethod of manufacturing according to claim 34, wherein the laserimpression is a product number.
 41. The method of manufacturingaccording to claim 34, wherein the laser impression is a company name.42. The method of manufacturing according to claim 34, wherein the laserimpression is a serial number.